1. Field of the Invention
This invention relates to a chemically amplified positive resist composition which is highly sensitive to actinic radiation such as deep-UV, electron beam and X-ray, developable with aqueous base to form a pattern, and suitable for fine processing.
2. Prior Art
As the LSI technology tends toward higher integration and higher speed, further refinement of pattern rules is required. The current patterning technology mostly relies on light exposure which is now approaching to the essential limit of resolution which is dictated by the wavelength of a light source. It is generally recognized that in light exposure using g-line (wavelength 436 nm) or i-line (wavelength 365 nm) as a light source, a pattern rule of about 0.5 .mu.m is the limit. For LSIs fabricated by such light exposure technique, a degree of integration equivalent to 16 mega-bit DRAM is the limit. At present, LSIs fabricated in the laboratory have reached this stage. It is urgently required to develop a finer patterning technique.
Under such circumstances, deep-ultraviolet lithography is regarded promising as the next generation of fine patterning technology. The deep-UV lithography is capable of working on the order of 0.3 or 0.4 .mu.m and makes it possible to form a resist pattern having a side wall nearly perpendicular to the substrate if a less light absorbing resist material is used. Advanced engineers place focus on the utilization of a high illuminance KrF excimer laser (wavelength 248 nm) as a deep-UV source. A resist material having low light absorption and high sensitivity must be developed before such an excimer laser can be used in a mass scale manufacturing technique.
From this point of view, a number of chemically amplified positive working resist materials using acid catalysts were recently developed as disclosed in U.S. Pat. Nos. 4,491,628, 5,310,619 and 5,362,607. These materials have high sensitivity, resolution and dry etching resistance and are promising as resist materials especially suited for deep-UV lithography. The chemically amplified, positive resist materials being known include those of the two-component system comprising an alkali-soluble base resin and a photoacid generator and those of the three-component system comprising an alkali-soluble base resin, a photoacid generator, and a dissolution inhibitor having an acid labile group. For these resist materials, it is desired to improve footing on nitride film substrates and post exposure delay (PED).
EP 679951 discloses a positive resist composition comprising a mixture of a polyhydroxystyrene having 10 to 60 mol% of the hydroxyl groups replaced by tert-butoxycarbonyl groups and a polyhydroxystyrene having 10 to 60 mol% of the hydroxl groups replaced by acetal groups and an organic carboxylic acid. This composition has the drawback of low resolution due to the use of a polymer mixture. Additionally, the composition is difficult to coat uniformly because many organic carboxylic acids such as monovalent or polyvalent aliphatic carboxylic acids, alicyclic carboxylic acids, unsaturated aliphatic carboxylic acids, oxycarboxylic acids, alkoxycarboxylic acids, and ketocarboxylic acids are less compatible with the polymers due to the absence of a phenyl group. Of the organic carboxylic acids, benzoic acid derivatives cannot be added in amounts of more than 1% by weight based on the weight of the resin component and photoacid generator combined because they show significant absorption at wavelengths of about 248 nm and reduce the transmittance and resolution of resists. For these reasons, the composition of EP 679951 is least effective for improving the footing on nitride film substrates and PED.